This proposal describes an experimental approach to study the role of the hormone relaxin in gestation and parturition. Specific projects include: 1) employ preparative isoelectric focusing to isolate pure bioactive relaxin fractions from pregnant rats, guinea pigs, and rabbits; 2) characterize the fractions both chemically and immunologically; 3) use of radioimmunoassay to study levels of the hormone in sera and tissues from normal and experimentally altered animals; 4) identify cells and tissues that contain relaxin by employing immunocytochemical techniques.